Overheating Question

[johnrolf]

I just replaced the impeller on my 1972 35hp chrysler model 354HC, due to a pretty bad overheat. The impeller was ground to bits. I ordered the impeller (sierra part #3084) that supposedly fits my motor. The old impeller had 6 fins, and the new impeller has 10. The new impeller's fins were too long, so I trimmed off the ribs on the end of each fin so it would fit snug into the water pump housing. It seems to be pumping water, but I'm not sure if this will be efficient enough. I took the boat for a test run and it didn't seem to overheat, but it didn't give a steady output of water out of the exhaust either. Sometimes it shoots out like a water hose, other times, it looks like just smoke or steam. I also removed the thermostat cover to find that there was no thermostat in the housing. What do I need to do to make sure that my engine is cooling properly? Is my "trimmed impeller" going to work ok? Shouldn't there be a thermostat inside the housing?

 

[scotiany]

Re: Overheating Question

I'd buy another impeller and NOT trim it. My 1970 55hp has 12 fins and it's very probably the same one that came with yours originally. Get a 143 deg thermostat. Running without a thermostat will cause overheating according to my Chilton's Chrysler manual.

 

[BF]

Re: Overheating Question

Hiya & welcome!<br /><br />ditto on the "buy a new impeller" advice. Trimming to fit is not good. I don't know your particular model of motor, but the vanes on the impeller usually have to be bent over quite a bit to fit into the water pump housing. You have to turn the driveshaft & impeller clockwise (looking from the top) as you push the pump housing on to make sure that you get all the vanes bent the correct way. Put some dish soap in the housing to lube the impeller for this and for initial start up.<br /><br />Buying a service manual would be a VERY good (almost essential) investment for you. You can get a seloc or similar that covers your motor. <br /><br />What caused your original impeller to get ground up? You do know that you should NEVER start an OB out of the water, right? The impeller will roast & disintegrate in seconds. If you wanna start it off the lake, you can put the leg in a barrel/garbage can of water or buy an attachment so your garden hose can supply water to the water intake.<br /><br />good luck.<br /><br />Brent

 

[BF]

Re: Overheating Question

oh, and when you have the lower unit off, you might wanna put a garden hose on the water tube running to the motor to make sure that the water passages in the motor aren't blocked by hunks of the impeller that disintegrated. If you're taking the thermostat cover off, you can flush it from there too.<br /><br />Brent

 

[johnrolf]

Re: Overheating Question

Thanks, I didn't know that the vanes were suppose to be bent inside the housing. Is that right? So the vanes are supposed to always be bent?

 

[BF]

Re: Overheating Question

yup... when the motor is turning (clockwise looking down at the flywheel) the tips of the impeller should be trailing inside the housing. That's why you turn the driveshaft the same way when you're fitting the impeller in the cup. If you get it wrong, for some motors there is enough room that the vanes will flip around and correct themselves, but for others there's not enough room in the housing for to allow them to flip and they just won't pump water as well. <br /><br />The manual will have pictures of all this.<br /><br />Brent